The present invention relates generally to wake-up functions for electronic circuits and, more particularly, to waking-up a microprocessor of a battery-operated semiconductor device from a sleep mode in response to an analog input signal exceeding a digitally programmed threshold level.
Certain semiconductor devices such as microcontrollers generally include a microprocessor core embedded with other components, such as timer circuits and ROM and RAM memory, on an integrated circuit (IC) chip. Microcontrollers are used in various applications, in hand held instruments, for example, such as tiny pocket-sized pagers, where the microcontroller interprets received characters, produces a signal such as a beep or vibration to notify the user of an incoming message, and displays multiple messages typically on a liquid crystal display (LCD). Other examples of microcontroller applications are use for controlling keyboards of personal computers, including to off-load many tasks formerly handled by the processor; in modems for command interpretation and data transmission; in printer buffers for storing and high speed dumping of data for driving the printer at low speed; in color plotters; color copiers; electronic typewriters; cable television terminal equipment; lawn sprinkling controls; credit card phone equipment; automotive applications such as engine control modules, anti-lock braking systems (ABS), and automobile suspension control for designating ride softness; to name some of the more popular applications.
In general, the microcontroller is battery-operated, with a microprocessor core that executes considerable internal instructions and performs numerous operations each second at its supplied clock rate. It is desirable to conserve power when the microprocessor is not being used, and typically this is done by suspending the operation of the microprocessor clock in what is commonly referred to as the "sleep" mode. The microprocessor may be exited or awakened, or "wake-up", from the sleep mode in response to the occurrence of one or more conditions. For example, the wake-up of the microprocessor may be in response to (I) an external reset signal being in a predetermined logic state; (ii) a watchdog timer, or any other timer, timing out; (iii) an interrupt signal occurring at an external pin; or (iv) a signal initiated manually by a user.
One technique for waking-up a microprocessor is disclosed in U.S. Pat. No. 5,315,549 to Scherpenberg et al which describes alternately enabling and disabling a sleep mode in response to an external logic signal. In particular, a memory controller for supplying backup battery power is disclosed having a sleep mode operation that is enabled when a logic signal is a logic low which turns off a field effect transistor and isolates the power output node. And when the logic signal is a logic high, the sleep mode is disabled because the field effect transistor is turned on and a battery node is connected to the power output node.
In U.S. Pat. No. 5,241,680 to Cole et al, a method and apparatus are disclosed for configuring a computer in a low-power mode, and in which the user can enter the full-power mode in a way that allows continuing with the application at the point just before entering the low-power mode. The latter mode is entered by saving an interrupt mask and by disabling interrupts, followed by saving the direct memory access (DMA) status, finishing DMA operations, and disabling DMA. After these steps, the I/O state of the machine is saved in various I/O registers and ports. A refresh of the memory is forced before the system refresh operations are discontinued.
In U.S. Pat. No. 5,117,500 to Davis et al, a battery powered receiver is disclosed including an adaptive signal decoder having means to conserve energy of the battery. The conservation means acts to disable a gated clock signal which disables most of the decoder if the bit rate search procedure fails to find an appropriate digital signal after several attempts. The decoder is implemented in CMOS logic elements, so that disabling the clock signal acts to reduce the power down by the decoder, to conserve the energy in the battery.
Neither these examples nor any other prior art of which the applicants are aware discuss waking-up a microprocessor from a sleep mode in response to an analog input signal exceeding a digitally programmable threshold level.
It is therefore a principal object of the present invention to provide a semiconductor device such as a microcontroller or microprocessor which is awakened from a sleep mode in response to an analog input signal which exceeds a digitally programmed threshold level.